FLUID REGULATORY HORMONE RESPONSE TO EXERCISE AFTER COCA-INDUCED BODY-FLUID SHIFTS

To determine the effect of coca chewing on heart rate (HR), mean arter ial blood pressure (MAP), and plasma volume and their relationship wit h the hormones regulating cardiovascular and body fluid homeostasis, 1 6 male volunteers were examined at rest and during 1 h of cycle exerci se at similar to 75% of their peak oxygen uptake in two trials separat ed by 1 mo. One trial was performed after the subjects chewed a sugar- free chewing gum (Coca(-) trial), whereas the other was done after the subjects chewed 15 g of coca leaves (Coca(+)), with the order of the Coca(-) and Coca(+) trials being randomized. Blood samples were taken at rest, before (R-1) and after 1-h chewing (R-2), and during the 5th, 15th, 30th, and 60th min of exercise. They were analyzed for hematocr it, hemoglobin concentration, red blood cell count, plasma proteins, a nd for the fluid regulatory hormones, including plasma catecholamines [norepinephrine (NE) and epinephrine], renin, arginine vasopressin, an d the atrial natriuretic peptide (ANP). During the control trial (Coca (-)), from R-1 to R-2, there was no significant change in hematologic, hormonal, and cardiovascular status except for a small increase in pl asma NE. In contrast, it can be calculated that coca chewing at rest i nduced a significant hemoconcentration (-3.8 +/- 1.3% in blood and -7. 0 +/- 0.7% in plasma volume), increased NE and MAP, and reduced plasma ANP. Chewing coca before exercise reduced the body fluid shifts but e nhanced HR response during exercise. These effects were not accompanie d by changes in NE, epinephrine, renin, and arginine vasopressin plasm a levels. In contrast, plasma ANP response to exercise was lower durin g the Coca(+) trial, suggesting that central cardiac filling was reduc ed by coca use. It is likely that the reduction in body fluid volumes is a major contributing factor to the higher HR at any given time of e xercise after coca chewing.